Spasmodic dysphonia neurological based?

SD is formally classified as a movement disorder, one of the focal dystonias, and is also known as laryngeal dystonia.  Supporting evidence that SD is a neurological disorder includes:

  •  SD may co-occur with other neurological movement disorders such as blepharospasm (excessive eye blinking and involuntary forced eye closure), tardive dyskinesia (involuntary and repetitious movement of muscles of the face, tongue, body, arms and legs), oromandibular dystonia (involuntary movements of the jaw muscles, lips and tongue), torticollis (involuntary movements of the neck muscles), or tremor (rhythmic, quivering muscle movements).
  • Spasmodic dysphonia runs in some families and is thought to be inherited. Research has identified a possible gene on chromosome 9 that may contribute to the spasmodic dysphonia that is common to certain families.

Histological examination of the nerve to the vocal cords in patients with SD demonstrates that the percentage of abnormally thin nerve fibers was higher than in normal controls
Functional MRI signal is reduced in sensorimotor cortices associated with movement of the affected body part in laryngeal dystonia, supporting a dystonic basis for this voice disorder

Spasmodic dysphonia causes

The exact cause of spasmodic dysphonia (SD) is unknown.[1] According to the National Institute on Deafness and Other Communication Disorders, “research has revealed increasing evidence that most cases of spasmodic dysphonia are in fact neurogenic or having to do with the nervous system (brain and nerves).”[2]

SD is a neurological disorder rather than a disorder of the larynx, and as in other forms of dystonia, interventions at the end organ (i.e., larynx) have not offered a definitive cure, only symptomatic relief. The pathophysiology underlying dystonia is becoming better understood as a result of discoveries about genetically based forms of the disorder, and this approach is the most promising avenue to a long-term solution.

Neurological cause or psychogenic?

The National Institute of Neurological Disorders and Stroke (NINDS) and the American Academy of Neurology (AAN) classify SD as a neurological disorder. However, because the voice can sound normal or near normal at times, some practitioners believe it to be psychogenic, that is, originating in the affected person’s mind rather than from a physical cause.

No medical organizations or groups take this position. A comparison of SD patients compared with vocal fold paralysis (VFP) patients found that 41.7% of the SD patients met the DSM-IV criteria for psychiatric comorbidity compared with 19.5% of the VFP group.

However, another study found the opposite, with SD patients having significantly less psychiatric comorbidity compared to VFP patients: “The prevalence of major psychiatric cases varied considerably among the groups, from a low of seven percent (1/14) for spasmodic dysphonia, to 29.4 percent (5/17) for functional dysphonia, to a high of 63.6 percent (7/11) for vocal cord paralysis.”

A review in the journal Swiss Medicine Weekly states that “Psychogenic causes, a ‘psychological disequilibrium’, and an increased tension of the laryngeal muscles are presumed to be one end of the spectrum of possible factors leading to the development of the disorder”.

Alternatively, many investigators into the condition feel that the psychiatric comorbidity associated with voice disorders is a result of the social isolation and anxiety that patients with these conditions feel as a consequence of their difficulty with speech, as opposed to the cause of their dysfluency. The opinion that SD is psychogenic is not upheld by experts in the scientific community

Spasmodic Dysphonia types

The three types of spasmodic dysphonia (SD) are adductor spasmodic dysphonia, abductor spasmodic dysphonia and mixed spasmodic dysphonia.

Adductor spasmodic dysphonia

In adductor spasmodic dysphonia (ADSD), sudden involuntary muscle movements or spasms cause the vocal folds (or vocal cords) to slam together and stiffen.These spasms make it difficult for the vocal folds to vibrate and produce voice. Words are often cut off or difficult to start because of the muscle spasms. Therefore, speech may be choppy but differs from stuttering. The voice of an individual with adductor spasmodic dysphonia is commonly described as strained or strangled and full of effort. Surprisingly, the spasms are usually absent while laughing, speaking at a high pitch, or speaking while singing, but singers can experience a loss of range or the inability to produce certain notes of a scale or with projection. Stress, however, often makes the muscle spasms more severe.

Abductor spasmodic dysphonia

In abductor spasmodic dysphonia, sudden involuntary muscle movements or spasms cause the vocal folds to open. The vocal folds cannot vibrate when they are open. The open position of the vocal folds also allows air to escape from the lungs during speech. As a result, the voices of these individuals often sound weak, quiet and breathy or whispery. As with adductor spasmodic dysphonia, the spasms are often absent during activities such as laughing or singing, but singers can experience a loss of range or the inability to produce certain notes of a scale or with projection.

Mixed spasmodic dysphonia

Mixed spasmodic dysphonia involves both muscles that open the vocal folds and those that close them and therefore has features of both adductor and abductor spasmodic dysphonia